The present invention relates to multi-wavelength, all-optical, regenerators for use in high speed optical communication systems, and to a method for regenerating an optical N wavelength division multiplexed channel signal received by a regenerator.
Conventional regenerators that are used in optical networks convert received optical signals to electronic signals and then back to optical signals for transmission to a next regenerator or terminal station. The problem with such conventional type of regenerators is that they have a bandwidth which is limited to 10 gigahertz and each channel has to be processed on a channel-by-channel basis. As point-to-point transmission speeds in communication systems approach 10 gigabits/second (e.g., in OC-192 systems) and beyond, it is highly desirable to use all-optical regenerators to extend transmission distances between regenerators (repeaters) instead of using the conventional type of regenerators that convert received optical signals to electronic signals and then back to optical signals. From a network point of view, the conventional electronic type of regenerators become bottlenecks for high capacity optical networks. In contrast, all-optical regenerators can provide a larger bandwidth and have many advantages when considering network scalability, management, and capacity. Therefore, all-optical regenerators will be key components for future all-optical communication networks.
It is desirable to provide a regenerator system and a method which simultaneously reamplifies, retimes, and reshapes received multiple wavelength division multiplexed channels entirely in the optical domain before retransmission along a next section of an optical communication system.
The present invention is directed to multi-wavelength all-optical regenerators, where each regenerator reamplifies, retimes, and reshapes multiple wavelength channels in a received N wavelength division multiplexed optical channel signal entirely in the optical domain.
Viewed from one aspect, the present invention is directed to an optical regenerator for use in an optical transmission system comprising an optical N wavelength division multiplexed channel signal synchronizing arrangement, an optical pulse retiming and reshaping arrangement comprising a nonlinear optical loop mirror (NOLM) arrangement, and an Erbium-doped fiber amplifier (EDFA). The optical N wavelength division multiplexed channel signal synchronizing arrangement is responsive to the reception of an optical input signal to the regenerator comprising N wavelength division multiplexed channel signals for synchronizing the phase of all of the N channel signals, and for generating an optical output signal comprising synchronized N wavelength division multiplexed channel signals, where Nxc2x72. The nonlinear optical loop mirror (NOLM) arrangement in the optical pulse retiming and reshaping arrangement is responsive to the optical output signal from the signal synchronizing arrangement for retiming and reshaping optical pulses of the optical synchronized N wavelength division multiplexed channel signals, and for generating a corresponding optical NOLM output signal. The Erbium-doped fiber amplifier (EDFA) amplifies the optical NOLM output signal, and generates an amplified and phase-synchronized optical N wavelength division multiplexed channel output signal for transmission as an output signal from the optical regenerator.
Viewed from another aspect, the present invention is directed to an optical regenerator for use in an optical transmission system comprising an optical wavelength division demultiplexer (WDD), a plurality of Nxe2x88x921 selectively changeable optical delays, an optical wavelength division multiplexer (WDM), an optical pulse retiming and reshaping arrangement comprising a nonlinear optical loop mirror (NOLM) arrangement, and an Erbium-doped fiber amplifier (EDFA), where Nxc2x72. The WDD is responsive to an optical input signal to the regenerator comprising N wavelength division multiplexed channels for directing the N channels onto separate N output paths. Each of the plurality of Nxe2x88x921 selectively changeable optical delays is coupled in a separate predetermined one of Nxe2x88x921 output paths of the WDD. Still further, each selectively changeable optical delay is responsive to a delay control signal for selectively adjusting the phase of the channel signal propagating in an associated one of an Nxe2x88x921 output path so that all Nxe2x88x921 optical channel signals are synchronized in phase with an Nth optical channel signal. The WDM multiplexes the Nth optical channel signal and the Nxe2x88x921 optical channel signals from the plurality of Nxe2x88x921 optical delays into a synchronized N wavelength division multiplexed channel optical output signal. The phase controller is responsive to a portion of the output signal from the WDM for detecting a phase difference between the Nth channel signal and each of the remaining Nxe2x88x921 delayed channel signals. In turn, the phase controller generates a separate delay control signal to each of the optical delays for synchronizing the phase of each of the Nxe2x88x921 delayed optical channel signals to the phase of the Nth optical channel signal. The optical pulse retiming and reshaping arrangement comprising a nonlinear optical loop mirror (NOLM) arrangement which is responsive to the optical output signal from the WDM for retiming and reshaping optical pulses of the optical synchronized N wavelength division multiplexed channel signals and for generating a corresponding optical NOLM output signal. The EDFA amplifies the NOLM output signal, and generates an amplified and phase-synchronized optical N wavelength division multiplexed channel output signal for transmission as an output signal from the optical regenerator.
Viewed from still another aspect, the present invention is directed to an optical regenerator for use in an optical transmission system comprising an optical N wavelength division multiplexed channel signal synchronizing arrangement, an Erbium-doped fiber amplifier (EDFA), and an optical pulse retiming and reshaping arrangement comprising a nonlinear optical loop mirror (NOLM) arrangement, a clock recovery circuit, and a laser. The optical N wavelength division multiplexed channel signal synchronizing arrangement is responsive to the reception of an optical input signal to the regenerator comprising N wavelength division multiplexed channels for synchronizing the phase of all of the N channel signals, and for generating an optical synchronized N wavelength division multiplexed channel output signal, where Nxc2x72. The nonlinear optical loop mirror (NOLM) arrangement is responsive to the optical output signal from the signal synchronizing arrangement for retiming and reshaping optical pulses of the N channel signals, and for generating a corresponding optical NOLM output signal. The clock recovery circuit is responsive to a predetermined one of the N channel signals propagating in the optical synchronizing arrangement for generating a clock output signal having a frequency corresponding to the bit rate frequency of the predetermined one of the N channel signals. The clock recovery circuit is also responsive to an output signal from the optical regenerator comprising N phase-synchronized optical N channel signals for synchronizing the phase of the clock output signal to the phase of the N channel signals in the output signal from the optical regenerator. The laser is responsive to the clock output signal from the clock recovery circuit for generating a corresponding optical clock output signal which is coupled into the NOLM. The Erbium-doped fiber amplifier (EDFA) is used to amplify the optical NOLM output signal, and generate an amplified and phase-synchronized optical N wavelength division multiplexed channel output signal for transmission as the output signal from the optical regenerator.
Viewed from still another aspect, the present invention is directed to a method of regenerating a received optical N wavelength division multiplexed channel signal in an optical regenerator of an optical transmission system, where Nxc2x72, comprising the following steps. In a first step, the phase of all of the N channel signals in the received optical N wavelength division multiplexed channel signal are concurrently and separately synchronized for generating an optical output signal comprising N synchronized wavelength division multiplexed channel signals. In a second step, the optical output signal from step (a) is split into two halves in an optical coupler so that a first half propagates in a first direction around an optical fiber loop wherein at least a portion thereof comprises a high nonlinearity optical fiber section and a second half propagates in a second opposite direction around the optical fiber loop. In a third step, an optical clock output signal from a laser is multiplexed with the first half signal propagating in the first direction in the optical fiber loop in the second step in an optical wavelength division multiplexer. This shifts the phase of the first half signal in the optical fiber loop by a predetermined amount and causes the first and second halves of the N channel signals to be switched out of a second port of the optical coupler as a NOLM output signal when the two halves return to the entry point of the optical fiber loop. In a fourth step, the optical NOLM output signal from the third step is amplified in an Erbium-doped fiber amplifier (EDFA) for generating an amplified and phase-synchronized optical N wavelength division multiplexed channel output signal for transmission as an output signal from the optical regenerator.
The invention will be better understood from the following more detailed description taken with the accompanying drawings and claims.